1. Field of the Invention
The invention relates to a transmission and reception device for a mobile radio base station comprising a plurality of transmission and reception units and hence a plurality of carriers, the transmission and reception units being accommodated in push-in modules and each having a modulator, a channel frequency device and an output stage.
2. Description of Related Art
A mobile radio base station usually serves a plurality of radio cells arranged sectorally with respect to the base station. Normally, three radio cells are provided per base station. Each radio cell has a plurality of associated transmission and reception devices, for example four such units. The possibility of diversity reception means that one radio cell normally has two antennas which are also used for transmission. In the example quoted, two transmission and reception units operate on one antenna. To enable this, so-called hybrid combiners are in use. When the carriers are combined, losses of 3 dB occur, which amounts to half the consumed power. A normal transmitter output power is 40 W per transmission and reception unit. The losses are accordingly considerable and are converted to heat in a load resistor. The hybrid combiners themselves are accommodated in particular individual push-in units. Each antenna additionally requires a duplex filter in order to separate the transmission and reception frequencies from one another.
In the example quoted, there are thus twelve transmission and reception units at the base station, which are accommodated in a so-called cabinet which is fully utilized.
In practice, the growing interest in mobile radio has resulted in a further increase in the number of carriers per cell. This can be achieved by means of a second fully stocked cabinet next to the first cabinet, so that the number of carriers is increased to twenty-four in the example given. For service providers, this solution has the disadvantage that their rental costs are increased.
When a mobile network is set up, there are initially few cells and a small number of carriers, and it is therefore necessary to operate at high transmitter output power in order to cover the relatively large cells. If the number of subscribers increases, then both the number of radio cells and the number of carriers per radio cell are increased. These radio cells are smaller and can be served at a lower transmitter output power.